The present invention relates to an improvement in a detection apparatus for detecting sizes of documents such as originals by means of a plurality of optical sensors which utilize reflected or transmitted light.
In duplicating an original with an electrophotographic copying machine or the like, it is usually the case to detect the size of the original mounted on the original table and to automatically select the copying paper having a size corresponding to the detected size.
The original size detection apparatus is structured such that light emitting devices and photodetector devices are arranged to receive light reflected from the original document or light transmitted therethrough and to thereafter determine the size of the original based on the conditions detected by the photodetector devices.
In the document size detection apparatus, the signal level of the detection signal have to be manually adjusted depending on the quantity of light from the light emitting devices, characteristics of the output level of the photodetector devices, characteristics of the circuits using these devices, etc. Much labor is required for making such adjustments. Besides, there is the need for readjustments during the use of the apparatus as the document table becomes dirty, the optical system including the light emitting devices and photodetector devices become dirty, or changes in the circuit characteristics occur.